S1B6-02 Issues on comfortability using Head-Mounted Displays

Virtual reality technologies, including head-mounted displays (HMD), can provide benefits to psychological research by combining high degrees of experimental control with improved ecological validity. This is due to the strong feeling of being in the displayed environment (presence) experienced by VR users. As of yet, it is not fully explored how using HMDs impacts basic perceptual tasks, such as object perception. In traditional display setups, the congruency between background environment and object category has been shown to impact response times in object perception tasks. In this study, we investigated whether this well-established effect is comparable when using desktop and HMD devices. In the study, 21 participants used both desktop and HMD setups to perform an object identification task and, subsequently, their subjective presence while experiencing two-distinct virtual environments (a beach and a home environment) was evaluated. Participants were quicker to identify objects in the HMD condition, independent of object-environment congruency, while congruency effects were not impacted. Furthermore, participants reported significantly higher presence in the HMD condition.

This chapter introduces design and principles of head mounted displays (HMDs), as well as their state-of-the-art examples, for augmented reality (AR). Section 2 introduces a brief history of head mounted displays, human vision system, and application examples of see-through HMDs. Section 3 describes designs and principles of HMDs, such as typical configurations of optics, typical display elements, and major categories of HMDs. Section 4 gives typical characteristics of HMDs, such as resolution, field of view, and distortion. Section 5 describes human perceptual and health issues such as depth perception and safety. Finally, Section 6 gives conclusions with future challenges and prospects. For researchers, learners and HMD developers, this chapter is a good start point to learn basics, state of the art technologies, and future research directions of HMDs. For system developers and end-users, this chapter will give a good insight to HMDs to choose a suitable HMD for their purposes.

Use of head-mounted displays (HMDs) and hand-held displays (HHDs) may affect the effectiveness of stability control mechanisms and impair resistance to falls. This study aimed to examine whether the ability to control stability during locomotion is diminished while using HMDs and HHDs. Fourteen healthy adults (21–46 years) were assessed under single-task (no display) and dual-task (spatial 2-n-back presented on the HMD or the HHD) conditions while performing various locomotor tasks. An optical motion capture system and two force plates were used to assess locomotor stability using an inverted pendulum model. For perturbed standing, 57% of the participants were not able to maintain stability by counter-rotation actions when using either display, compared to the single-task condition. Furthermore, around 80% of participants (dual-task) compared to 50% (single-task) showed a negative margin of stability (i.e., an unstable body configuration) during recovery for perturbed walking due to a diminished ability to increase their base of support effectively. However, no evidence was found for HMDs or HHDs affecting stability during unperturbed locomotion. In conclusion, additional cognitive resources required for dual-tasking, using either display, are suggested to result in delayed response execution for perturbed standing and walking, consequently diminishing participants’ ability to use stability control mechanisms effectively and increasing the risk of falls.

Head mounted displays (HMDs) are being explored as an alternative means of displaying relevant information to dismounted operators. The goal of this project was to examine different visual display concepts and evaluate participant’s attention allocation to information presented on their HMD. Additionally, their ability to detect potential threats in the environment was also evaluated. This information will help revamp the design of information displays for HMDs. The task in this study required participants to monitor their HMD for critical alerts and respond accordingly while also making shoot/no shoot decisions to threats in their environment. We hypothesized that as information is presented in different layouts on the HMD, it will reduce the participants’ ability to detect real world events. Accuracy of the shoot/no shoot decisions was collected along with accuracy of detection of information on the HMD. We found that shooting performance was not affected between the three HMD layouts however information detected on the HMD was worst when all information was in the center of the HMD. The data from this study will be used to help develop intelligent visual displays used by Battlefield Airmen to accomplish their mission.

Since the metaverse was introduced, virtual reality (VR) head-mounted displays (HMDs) are increasingly being used for VR gaming, sports and 3D films. Additionally, the Pancake optical module has made HMDs smaller and lighter, which greatly increased its comfortability. However, during real use, there will inevitably be a lot of user head mouvements, such as shaking, lowering and raising, etc., which will cause certain displacement of the HMDs due to its inertia. Then the relative displacement of HMDs may affect the pressure and pressure-bearing area of the head, which leads to user discomfort.Currently, the research on the comfort of HMDs primarily focuses on the static scenarios without mouvement. This paper investigated the relative displacement and user comfort of the HMDs in motion. The main purpose of this study is to determine the relationship between HMDs' displacement and the contact area in order to provide design guidances and insights for HMDs, particularly the binding area. This paper also proposed an effective experimental method for measuring the relative displacement of HMDs, which can be used to assess the dynamic stability.A simple VR environment was bulit to guide the participant’s head movements by moving circular lightened dots, for simulating the head mouvements in daily life. At the same time, a wearable ruler sticker was designed to measure the displacement of the HMDs relative to the head.The experimenter took measurements of participants’ heads and assisted them to get familiar with the HMDs, and then pasted ruler stickers on the participants’ faces. The participants put on the HMD and adjust it to a comfortable position. Then they completed the head movement under the guidance of the VR environment and repeated it for 5 times. The same procedure was repeated after changing the contact area of the binding with 40mm*40mm foam cotton pieces. The HMD’s position was recorded before and after the mouvement.The results shows that, the HMDs exhibit a significant displacement relative to the head, after performing typical head motions, which causes some slight discomfort. Meanwhile, after doing a data correlation with SPSS, it can be found that the contact area of the binding is one of the main reasons for HMDs’ displacement. And the displacement can be greatly reduced and the pressure comfort rarely changes when the contact area of the bindings is increased, which has a positive impact on the overall comfort evaluation. Besides, we believe that in addition to the contact area, the mass distribution, pressure, and materials also have an effect on the relative displacement of HMDs, which might be the focus of future research. In future, new prototypes will be developed to increase the accuracy of environmental variables control and the evaluation of different factors.

Virtual and physical worlds are merging. Currently users of head-mounted displays cannot have unobtrusive tactile feedback while touching virtual objects. We present a mid-air tactile feedback system for head-mounted displays. Our prototype uses the focus of a modulated ultrasonic phased array for unobtrusive mid-air tactile feedback generation. The array and the hand position sensor are mounted on the front surface of a head-mounted virtual reality display. The presented system can enhance 3D user interfaces and virtual reality in a new way. To evaluate the tactile feedback together with visuals on an Oculus Rift VR headset, we had 13 participants do a simple virtual keypad tapping task with and without tactile feedback. The results indicate that while the measured speed and accuracy differed only a little, the subjects were nearly unanimous in that they preferred to use the tactile feedback. The raw NASA TLX questionnaires conducted after use revealed that the participants felt slightly less mental, physical and temporal demand with the tactile feedback. The participants' self-assessment of their performance was also higher with the tactile feedback.

Background2D and 3D virtual reality platforms are used for designing individualized training environments for post-stroke rehabilitation. Virtual environments (VEs) are viewed using media like head mounted displays (HMDs) and large screen projection systems (SPS) which can influence the quality of perception of the environment. We estimated if there were differences in arm pointing kinematics when subjects with and without stroke viewed a 3D VE through two different media: HMD and SPS.MethodsTwo groups of subjects participated (healthy control, n = 10, aged 53.6 ± 17.2 yrs; stroke, n = 20, 66.2 ± 11.3 yrs). Arm motor impairment and spasticity were assessed in the stroke group which was divided into mild (n = 10) and moderate-to-severe (n = 10) sub-groups based on Fugl-Meyer Scores. Subjects pointed (8 times each) to 6 randomly presented targets located at two heights in the ipsilateral, middle and contralateral arm workspaces. Movements were repeated in the same VE viewed using HMD (Kaiser XL50) and SPS. Movement kinematics were recorded using an Optotrak system (Certus, 6 markers, 100 Hz). Upper limb motor performance (precision, velocity, trajectory straightness) and movement pattern (elbow, shoulder ranges and trunk displacement) outcomes were analyzed using repeated measures ANOVAs.ResultsFor all groups, there were no differences in endpoint trajectory straightness, shoulder flexion and shoulder horizontal adduction ranges and sagittal trunk displacement between the two media. All subjects, however, made larger errors in the vertical direction using HMD compared to SPS. Healthy subjects also made larger errors in the sagittal direction, slower movements overall and used less range of elbow extension for the lower central target using HMD compared to SPS. The mild and moderate-to-severe sub-groups made larger RMS errors with HMD. The only advantage of using the HMD was that movements were 22% faster in the moderate-to-severe stroke sub-group compared to the SPS.ConclusionsDespite the similarity in majority of the movement kinematics, differences in movement speed and larger errors were observed for movements using the HMD. Use of the SPS may be a more comfortable and effective option to view VEs for upper limb rehabilitation post-stroke. This has implications for the use of VR applications to enhance upper limb recovery.

We present a user performance analysis of four navigation systems based on different visualization schemes (2D, 3D, stereoscopy on a monitor, and a stereo head mounted display (HMD)). We developed a well-defined user workflow, which starts with the selection of a safe and efficient needle path, followed by the placement, insertion and removal of the needle. We performed the needle procedure on a foam-based phantom, targeting a virtual lesion while avoiding virtual critical structures. The phantom and needle's position and orientation were optically tracked in real-time. 28 users performed each a total of 20 needle placements, on five phantom configurations using the four visualization schemes. Based on digital measurements, and on qualitative user surveys, we computed the following parameters: accuracy and duration of the procedure, user progress, efficiency, confidence, and judgment. The results show that all systems are about equivalent when it comes to reaching the center of the target. However the HMD- and 2D- based systems performed better in avoiding the surrounding structures. The needle procedures were performed in a shorter amount of time using the HMD- and 3D- based systems. With appropriate user training, procedure time for the 2D- based system decreased significantly.

During the last few years head mounted displays (HMD) became more important in Computer assisted surgery (CAS). Rapid head movements of the surgeon enforce to change the focal plane and the zoom value without loosing the calibration. Starting from previous work in developing an optical see through head mounted display we adapted our HMD to measure the focal and zoom values. This made it possible to extend the calibration to different zoom and focus values. The case of the HMD was opened to gain access to the zoom lenses, which was necessary to measure the different zoom values. Focusing in our HMD is realized by changing the angle between the two tubes. Therefore we marked two points at the tubes to measure the focal adjustment. We made a series of planar calibrations with seven different fixed zoom and focus values using Tsai´s algorithm for camera calibration. Then we used the Polaris optical tracking system (Northern Digital, Ontario, Can) to measure the transformation from the planar calibration grid to a tracker probe rigidly mounted to the HMD. The calibration parameters transformed to this tracker probe are independent of the actual position of the calibration grid andare the parameters we want to approximate. Then least square approximating polynomial surfaces were derived for the seven calibration parameters. The coefficients of the polynomial surfaces were used as starting values for a nonlinear optimization procedure minimizing an overall error. Minimizing the object space error (which is the minimal distance of the line through the center of projection and the image point to the real world point) in the last step of the procedure described above we had a mean object space error 0.85 ±0.5 mm. Calibration of the HMD is not lost during minor changes in zoom and focus. This is likely to be the first optical see through HMD developed for CAS with variable zoom and focus, which are typically facilities of operating microscopes. Employing an automated calibration in common with more zoom and focus steps and more accurate measurement of the position of the zoom lenses and the focal plane should reduce the error significantly, enabling the accuracy needed for CAS.

Head mounted displays (HMDs) can present visual information to operators at times when this would otherwise be difficult or impossible using standard visual displays. HMDs have been shown to benefit anesthetists in simulated medical environments. Operators, however, may have trouble extracting information from the HMD in dynamic environments. Operators may also fail to consciously perceive visual events that are important, meaningful, or bizarre if attending to other aspects of the visual scene. We investigated how attention manipulations (Focused, Divided, Just Watch) interact with display type (HMD, Standard Display) and found that participants were less likely to detect unexpected events using the HMD. We also found that unexpected event detection decreased from the Just Watch to Divided to Focused attention conditions. We suggest further testing be taken to ensure that HMDs to not result in failures to detect unexpected events in anesthesia monitoring.

This paper describes a head mounted display (HMD) which can present visual images with high reality using the characteristics of the human eye. The HMD has received considerable attention as vision presentation equipment for virtual reality or telerobotics. However conventional HMDs have problems that those images are narrow view angle and low resolution, because those displays have a fixed number of scanning lines. In order to improve it, an eye movement tracking type HMD (EMT-HMD) was proposed. The EMT-HMD can present wider view angle and higher resolution compared with the conventional HMDs, though conventional display devices are used. The principle is that a small high resolution image is superimposed on a wide low resolution image using two conventional display devices. A small, high resolution image is presented at small area around the view point according to the output of the eye movement detector. On the other hand, a wide, low resolution image is presented at its peripheral wide area. In this paper, the structure which can track eye movement in 2-dimension is discussed. Then, the structure of the trial production system, is explained. Also, some evaluation experiments are be introduced to confirm the effectiveness of the proposed idea.

Head Mounted Displays (HMDs) are the most popular devices for virtual reality, telexistence/telepresence humanoid operation, and remote behavior navigation. Telexistence/telepresence robot operation is an advanced teleoperation, enabling a human operator to perform remote dexterous manipulation tasks while having the feeling of being present in the remote environment. Behavior navigation is a novel technology that allows an expert to navigate a remote unskilled cooperator to perform general tasks. Since it is difficult to realize a large field of view (FOV) with an HMD, this has led to the development of immersive surround display systems. However, the fact that the operator's arms sometimes conceal the screen image of the surround display presents a serious drawback. To improve the performance of robot operation or remote behavior navigation in unknown environments, we propose the simultaneous utilization of a slimline HMD for central vision and a surround display for peripheral vision. Users of this novel display system can see the relatively high-resolution image on the display screens of the HMD, and their arms do not conceal the HMD image. In addition, users can see the large FOV image on the surround display around the HMD, although this may still be concealed by the user's arms. This enables full utilization of the natural and large FOV image. In this paper, we present the concept of a hybrid head mounted/surround display system, describe the configuration of a prototype setup, and present the results of a preliminary experiment.

Providing the warfighter with Head or Helmet Mounted Displays (HMDs) while in tracked vehicles provides a means to visually maintain access to systems information while in a high vibration environment. The high vibration and unique environment of military tracked and turreted vehicles impact the ability to distinctly see certain information on an HMD, especially small font size or graphics and information that requires long fixation (staring), rather than a brief or peripheral glance. The military and commercial use of HMDs was compiled from market research, market trends, and user feedback. Lessons learned from previous military and commercial use of HMD products were derived to determine the feasibility of HMDs use in the high vibration and the unique environments of tracked vehicles. The results are summarized into factors that determine HMD features which must be specified for successful implementation.

Remote operation of devices and monitoring can be supported by a combination of an actuated remote camera and a head-mounted display. This work considers the tracking control of a camera - head mounted display system over a communication network subject to delays. The objective is to design a control scheme such that the mismatch between the viewing direction of the head-mounted display and the camera is minimized. For the considered system the camera has a field of view and resolution which is larger than the one of the head-mounted display. The controller at the camera side guarantees that the mismatch of the viewing directions is below a specific bound. Furthermore, the remaining pointing mismatch is compensated by selecting and displaying the part of the image on the head-mounted display corresponding to the desired field of view. The proposed controller employs a prediction model. It is based on set-based methods to take the unknown future movement of the head into account. We outline conditions to guarantee bounded tracking errors in the presence of communication delays. Additionally, we outline how unnecessary communications and actuations can be avoided. The results are illustrated by simulations.

Head-mounted displays (HMDs) offer immersion and binocular disparity. This study investigated whether an HMD yields better object-alignment performance than a conventional monitor in virtual environments that are rich in pictorial depth cues. To determine the effects of immersion and disparity separately, three hardware setups were compared: 1) a conventional computer monitor, yielding low immersion, 2) an HMD with binocular-vision settings (HMD stereo), and 3) an HMD with the same image presented to both eyes (HMD mono). Two virtual environments were used: a street environment in which two cars had to be aligned (target distance of about 15 m) and an office environment in which two books had to be aligned (target distance of about 0.7 m, at which binocular depth cues were expected to be important). Twenty males (mean age = 21.2, SD age = 1.6) each completed 10 object-alignment trials for each of the six conditions. The results revealed no statistically significant differences in object-alignment performance between the three hardware setups. A self-report questionnaire showed that participants felt more involved in the virtual environment and experienced more oculomotor discomfort with the HMD than with the monitor.